Had sort of the same problem with my old T/C Hawkins 50 cal.Years ago sent it to a friend of mine to have engravings and ivory inlaid in stock. For some reason when I got it back it shot same PRB,powder load extremely high. This smokepole was a tackdriver prior to getting stockwork done. With rear site adjusted as low as it would go,still shot very high. I ended up removing front sight, welding a taller bead(doesn`t take much) on original site and dressing it down to my liking. Its again a tack driver with rear site adjusted in middle.